In digital communication systems, frequency selectivity and time variability in a transmission path arise because of multipath phasing caused by transmission signals being reflected by buildings or the like or Doppler variations caused by the movement of terminals. In such a multipath environment, a received signal becomes a signal in which a transmission symbol and a symbol arriving after a delay time interfere with each other.
For such a transmission path having frequency selectivity, a single carrier block transmission method has recently attracted attention in order to acquire the best receiving characteristics (see, for example, Non Patent Literature 1 listed below). A single carrier (SC) block transmission method can reduce the peak power compared with an OFDM (Orthogonal Frequency Division Multiplexing) transmission method, which is multi carrier (MC) block transmission (see, for example, Non Patent Literature 2 listed below).
With a transmitter that performs SC block transmission, measures against multipath phasing are taken by performing, for example, transmission as follows. First, after generating a PSK (Phase Shift Keying) signal or a QAM (Quadrature Amplitude Modulation) signal, which are digital modulation signals, in a “Modulator”, the digital modulation signal is converted to a time domain signal by a precoder and an IDFT (Inverse Discrete Fourier Transform) processing unit. Thereafter, as a measure against multipath phasing, a CP (Cyclic Prefix) is inserted by a CP insertion unit. The CP insertion unit copies a predetermined number of samples from the end of the time domain signal and adds the samples to the head of the transmission signal. In addition to this method, as a measure against multipath phasing, ZP (Zero Padding: zero insertion), in which zero is inserted into the front portion or the end portion of data, is performed.
Furthermore, in order to reduce the transmission peak power, in a transmitter that performs SC transmission, a precoder typically performs DFT (Discrete Fourier Transform) processing.